New techniques have been developed for identification of neurons in culture and for localization of viral antigen on vibratome sections of the nervous system. The maturation of a demyelinating mutant of mouse hepatitis virus in cultured nerve cells was found to be different from that of the wild type virus. Similarly, this mutant has a reduced tropism for neurons in vivo but specifically infects oligodendrocytes and causes progressive demyelination in mice. A chronic measles infection of spinal cord neurons has been characterized and all viral proteins are expressed but there is a lack of incorporation of capsids into the viral bud, which results in non-infectious virions. Rat Schwann cells, the myelin-forming cells of the peripheral nervous system, have been cultured, stimulated to mitosis, grown in large quantities and studied after multiple passages. They have preserved their characteristic motility, consisting of alternation of migration and undulation. Preliminary results seem to indicate that they are still able to myelinate. Schwann cells are susceptible to infection with rhabdovirus but an unusual pattern of viral expression was observed in these cells.